Custom field value not getting updated

I have created a plugin with message as send (Post condition), setEntity(Post condition) and SetStateDynamicEntity(Pre-condition) with primary entity as Email. When user send an email with or without attachment, i retrieved the actualEnd date from the email entity and update in the opportunity custom field as Last activity. It working fine in Non-prod environment, when we go for production it was not working. Please any one tell me what is the reason for this issue. And also please suggest me is there any outoffbox functionality to track the last activity date in the opportunity custom field.